The present invention comprises an improved seed supply system for a multiple row seed sower. This system is advantageous in that a uniform volume of seed is always made available to each sower unit, regardless of its position and distance from the seed source. In this way, if the supply of seed becomes exhausted during sowing operations, each sower unit will run out of seed essentially simultaneously.
Seed sowing devices having multiple sower units which are fed from a central seed hopper or reservoir are fairly well known for various agricultural applications. One example is shown in U.S. Pat. No. 4,145,980 to Boots. Here, a long drum is perforated around its circumference with a number of parallel rows of small holes. Pressure inside the drum is reduced so that as the drum rotates by a trough filled with seeds, the seeds are picked up by the holes. They are then transported to a planting location at which point the vacuum is temporarily broken to release the seed. A similar system is shown in U.S. Pat. No. 4,306,509 to Hassan, et al. and in West German application DE 30 03 919. U.S. Pat. Nos. 3,990,606 to Gugenhan and 4,241,849 to Harrer show individual sower units which can be used in ganged fashion. Each of these units has a separate seed hopper, however. One system known to applicant has sower units very similar to those shown in the previous two patents. These also have individual seed hoppers for each sower unit. However, the sower unit hoppers are apparently supplied from a single main seed hopper through seed supply ducts. This device is sold commercially as the Pneumasem II and is available from its manufacturer, Nodget Gougis, Montreau, France. The mechanism by which seed is transferred from the main hopper to the sower unit hoppers is not known to the present inventors. It does not appear to be by gravity since illustrations show loops in the seed supply ducts.
One problem with the use of a sower having individual sower unit hoppers is that it is impractical in the field to measure identical quantities of seed into each hopper. Situations arise where seed of a given species or family within a species is sown in relatively small lot numbers. An example might be the production of tree seedlings for reforestation. Land value in these nurseries is extremely high and it is essential that little or no growing space is wasted. Such waste occurs when planting a multiple row bed if the hoppers do not run out of seed essentially simultaneously. One source of difficulty with a device using a central seed hopper having seed tubes leading to the individual sower unit hoppers is the unequal volumes of seed contained within each line. Generally speaking, the outside sower unit hoppers will have more seed in inventory than will the inside sower unit hoppers. This is because of the greater volume of seed contained within the relatively longer ducts necessary to reach the outside hoppers. If the seed supply in the main hopper runs out, seed will continue to be sowed in the outer rows for a considerable distance after the point at which it has been exhausted in the inner rows. The present invention is a seed supply system that overcomes this deficiency. It maintains essentially equal volumes of seed in the supply provided for each sower unit. In this way, when the seed supply becomes exhausted, each row will end at substantially the same location.